The present invention relates to a magnetoresistive magnetic head (MR magnetic head) used in magnetic recording apparatus such as magnetic disk apparatus.
FIG. 1 is a front view showing a conventional MR magnetic head. This MR magnetic head comprises a substrate 1, an insulating layer 2 disposed on the substrate 1, a lower shield layer 3 disposed on the insulating layer 2, an insulating layer 4 as a lower reproduction gap formed on the lower shield layer 3, a magnetoresistive film 7 (MR film), a soft magnetic material film 5 for applying a transverse bias magnetic field to the MR film 7, an intermediate layer 6 for magnetically decoupling the soft magnetic material film 5 and MR film 7, an undercoating film 8 composed of Cr and others, a hard magnetic material film 9 for controlling the magnetic domain of the MR film, a conductive lead layer 10, an insulating layer 11 as an upper reproduction gap, an upper shield layer 12, an insulating film 13 for separating the reproducing head and recording head, a lower core layer 14 of recording head, an insulating layer 15 as a recording gap, an upper core layer 16 of recording head, and an insulating layer 17 as a protective layer.
In the case of this head, since the width of the recording track and the width of the reproducing track can be set individually, it is possible to record widely and reproduce narrowly. Besides, as the transverse bias system for keeping the linearity of the output, a method called Soft-Adjacent-Layer (SAL) bias. system is employed. In this SAL bias system, the soft magnetic material film 5 is magnetized by the magnetic field generated by a sense current flowing in the MR film 7, and a bias magnetic field is applied to the MR film 7 by the magnetic field generated from the magnetization of the soft magnetic material film 5. The hard magnetic material film 9 is to control the magnetic domain of the MR film 7 to form into a single magnetic domain in order to suppress the Barkhausen noise peculiar to the MR reproducing head.
In the MR film 7, by the magnetic flux getting from a magnetic recording medium into the MR film 7, especially by the magnetic flux getting vertically into the confronting surface of the magnetic recording medium, the direction of its internal magnetization is changed, and the electric resistance varies with the change of the direction of magnetization. Therefore, it is the MR reproducing head that picks up the change of this electric resistance as a signal and reproduces the data. In other words, when the direction of magnetization undergoes a large change as the magnetic flux enters, the reproduction output increases, so that the data can be reproduced more effectively.
By disposing the hard magnetic material film 9 magnetized in one direction, as shown in FIG. 2, the part of the MR film 7 facing the hard magnetic material film 9, that is, both end parts of the MR film 7 are magnetized opposite to the direction of magnetization of the hard magnetic material film 9. Besides, the middle part of the MR film 7, that is, the track portion T contributing most to the reproduction characteristic is magnetized in the same direction as the direction of magnetization of the hard magnetic material film 9. At this time, by being formed so that the direction of magnetization of the hard magnetic material film 9 may be parallel to the confronting surface of the magnetic recording medium, the magnetization of the track portion T may also be parallel to the confronting surface of the magnetic recording medium. Therefore, when a vertical magnetic flux enters the MR film 7, the direction of magnetization of the track portion T undergoes a large change, so that a large reproduction output is obtained.
In such an MR reproducing head, however, when the width TW of the track portion T is narrowed for downsizing the apparatus, a problem occurs because the reproduction output is decreased.
In the small-sized magnetic disk apparatus, since the individual servo head was not available, it was necessary to control the servo by using the MR reproducing head itself. However, since both ends of the track portion T are very unstable under magnetization, if the magnetic recording medium is out of the recording track, the linearity of the reproduction output is poor, and the servo performance is impaired. In particular, when the track width is narrow, the effect of the track end portions increases relatively, and hence the track density cannot be enhanced.